The present invention relates to industrial robot systems, and more particularly to a device for preventing an industrial robot system from operating abnormally due to factors such as variations in temperature.
An example of an industrial robot system operating in response to a prestored program is disclosed in Japanese Patent Publication No. 21362/1980. A conventional industrial robor system similar to that system will be described with reference to FIGS. 1 and 2.
In these figures, reference numeral 1 designates a first conveyor for supplying workpieces 2. A second conveyor 3, laid parallel to the first conveyor 1, supplys boxes 4. A third conveyor 5 crosses the first and second conveyors 1 and 3 at their ends; and a robot 6 is installed near the end of the third conveyor 5, and has a working range extending to the ends of the first and third conveyors 1 and 5.
In FIG. 2, 6a designates the base of the robot 6. A lifting mechanism 6b is installed on the base 6a and has an electric motor 6c. A first working body 6d is driven by the lifting mechanism 6b and has a lifting shaft which is lifted while being supported by the base 6a. A turning mechanism 6e is provided at the end of the first working body 6d and is energized by an electric motor. A second working body 6f includes an arm secured at one end to the turning mechanism 6e, for performing a turning operation. A turning mechanism 6g is provided at the free end of the second working body 6f and is energized by an electric motor. A third working body 6h has an arm secured at one end to the turning mechanism 6g, for performing a turning operation. A turning mechanism 6i provided at the free end of the third working body 6 and is energized by an electric motor. A gripping device 6j is secured to the operating part of the turning mechanism 6i. A control device 7 is provided for the robot 6.
The robot is controlled by the control device 7 according to a prestored program, whereby the first through third working bodies 6d, 6f and 6h perform their working operations with the aid of the lifting mechanism 6b and the turning mechanisms 6e and 6g, respectively, and the gripping device 6j conducts its working operation with the aid of the turning mechanism 6i, so that the workpieces 2 supplied by the first conveyor 1 are put in the box 4 supplied by the second conveyor 3. The box 4 containing the workpieces 2 is conveyed by the third conveyor 5.
In this industrial robot system, after the robot starts its operation, the electric motor for the turning mechanisms generate heat, causing the various working bodies to expand. Hence, since the control of the turning operations is based on turning angles, errors are caused in the working operation positions of the working bodies, with the result that the operation of the robot becomes inaccurate.